Two mass shootings claimed the lives of 31 people in the U.S. over the weekend.
A gunman opened fire inside a Wal Mart in El Paso, Texas, on Saturday, killing 22 and injuring 24.
Less than 24 hours later, police responded to a shooting outside of a popular bar in Dayton, Ohio. Nine people, including the gunman, were killed. Another 27 were injured.
Here’s what we know about the suspected gunmen:
El Paso, Texas
Police have identified the suspected gunman in the El Paso, Texas shooting as 21-year-old Patrick Crusius, of Allen, Texas.
On Monday, Crusius was charged with capital murder. According to police, he is being held without bond.
WATCH: El Paso shooting rampage treated as domestic terrorism
Federal authorities have been investigating the shooting as a case of domestic terrorism.
At a press conference on Monday, El Paso police chief Greg Allen told reporters that Crisuis has been cooperative, though he has shown “no remorse” and “appears to be in a state of shock and confusion.”
Police are also investigating a racist, anti-immigration “manifesto,” which was posted online on 8Chan prior to the massacre.
At a press conference on Sunday, Allen said authorities were investigating, and were working to determine whether the suspected gunman was, in fact, the author of the document.
“We have to attribute that manifesto directly to him,” Allen said. “And so we’re going down that road.”
WATCH: Death toll in El Paso shooting spree rises to 22
A Twitter account under Crusius’s name, that appeared not to have been updated since 2017, included a photo of Trump sitting at his desk in the Oval Office and a pro-Trump poll asking about the best way to secure the country.
The potential responses were the hashtags #BuildTheWall, #NoSanctuaryCities, #KeepGitmoOpen and #BanSyrianRefugees.
Crusius responded by tweeting ”#BuildTheWall is the best way that @POTUS has worked to secure our country so far!”
Crusius’ LinkedIn page, which has since been removed, listed a job bagging groceries.
“I’m not really motivated to do anything more than what’s necessary to get by,” the post reads. “Working in general sucks. … I spend about 8 hours every day on the computer so that counts toward technology experience I guess.”
Under skills, he posted, “Nothing really.”
WATCH: FBI say Dayton shooter sought out violent ideologies
In a statement, the suspect’s grandparents said they were “devastated” by the incident, and “pray for the victims of this tragedy.”
They said he had been living with them in a house in Allen, Texas, while he attended junior college at Collin College, but had moved out six weeks ago.
According to the statement, he had spent a few nights back at the home while they were out of town.
“His drivers license and mailing address were at our house in Allen — that connection has made us the focus of the media. We are talking only to law enforcement agencies and will not be making further statements to the media.”
WATCH: Ex-girlfriend of Dayton shooter says she missed warning signs
“We request the media to honor our privacy,” the statement said.
Court documents show the suspect’s mother had filed for divorce in 2011.
His mother has been a nurse in Texas since 1990. His father is a licenced counsellor.
Hours after the massacre in El Paso, Texas, 24-year-old Connor Betts opened fire outside of a popular bar Dayton, Ohio.
He was fatally shot by police less than a minute after killing eight people.
WATCH: Dayton gunman had troubled past, hit list
At a press conference on Tuesday, Dayton police Chief Richard Biehl said evidence gathered on Betts revealed he had an obsession with “violent ideation.”
“Materials reveiwed thus far reveal that the individual had a history of obsession with violent ideations that include mass shootings and expressed the desire to commit a mass shooting,” he said. “Subsequent material has revealed an orientation toward violent ideologies which elevate this case to one of federal interest.”
The FBI is now taking a “central role” in certain aspects of the case, Biehl said.
Officials said they still don’t know why Betts targeted Dayton, but said they had not found evidence to show the shooting was racially-motivated.
“We have not found anything that indicates that it is a racial motivation at this time,” said FBI special agent Todd Wickerham during the conference.
At a previous press conference on Sunday, police said there was nothing in the background of Betts that would have prevented him from purchasing a firearm.
WATCH: Former classmates of Dayton shooter says he threatened students, made ‘hit list’
“There’s nothing in this individual’s record that would have precluded him from getting these weapons,” Biehl told reporters.
However, in the wake of the shooting, former classmates have spoken out, indicating Betts had a troubled past and had been suspended twice during high school.
Two former classmates, who spoke to the Associated Press on the condition of anonymity out of concern they might face harassment, said Betts had been suspended during their junior year at Bellbrook High School after a “hit list” was found in the school’s bathroom.
Earlier, Betts had been suspended for arriving at school with a list of female students he wanted to sexually assault, his classmates said.
“There was a kill list and a rape list, and my name was on the rape list,” a female classmate told the Associated Press.
WATCH: Community of Dayton, Ohio asking ‘why?’ after shooter opens fire killing 9, injuring dozens
The woman said she didn’t really know Betts, and was surprised when a police officer called her during her freshman year to tell her that her name was on a list of potential targets.
“The officer said he wouldn’t be at school for a while,” she told the Associated Press, “But after some time passed he was back, walking the halls. They didn’t give us any warning that he was returning to school.”
The male classmate said most people avoided Betts and said he routinely threatened violence toward other students.
“He would say shocking things just to get a reaction,” he said. “He enjoyed making people feel scared.”
WATCH: Police confirm identity of Dayton mass shooter, victims
At a press conference on Sunday, Police Chief Richard Biehl said it would be “irresponsible” to suggest a potential motive in the early stages of the investigation.
It also remains unclear if Betts targeted his sister, 22-year-old Megan Betts, who was the youngest of those killed in the attack.
“It seems to just defy believability he would shoot his own sister, but it’s hard to believe that he didn’t recognize it was his sister, so we just don’t know,” Biehl said.
On Tuesday, Bellbrook police chief Doug Doherty read a statement on behalf of the Betts family.
In the statement, the family said they are “shocked” and “devastated” by the event, and offered their prayers and condolences to the families and friends of the victims.
WATCH: Betts family says in statement they’re ‘shocked and devastated’ by Dayton shooting
“The Betts family is cooperating with law enforcement in their investigation into this tragedy,” the statement said. “They respect the investigative process being conducted by the Dayton Police Department and the FBI and will not comment further on this investigation.”
The family also expressed their “enormous gratitude and love” for everyone who has reached out and given their support.
“They ask that everyone respect the family’s privacy in order to mourn the loss of their son and daughter, and to process the horror of Sunday’s events.”
Identifying mass shooters
James Densley is a professor of criminal justice at Metropolitan State University and has been studying violence in society, including mass shootings for the last two years.
Alongside psychologist Jillian Peterson, Densley founded the Violence Project, a study which looks at violence in society — including mass shootings.
They have also developed a database dating back to 1966 of every mass shooter who has shot and killed four or more people in a public place, and every shooting incident at schools, workplaces and places of worship since 1999.
In their research, Densley and Peterson have found a number of commonalities among the perpetrators of mass shootings.
In an interview with Global News on Tuesday, Densley said a trend he has seen in incidents of mass shootings is that they are often a “slow build over time.”
“You can trace it back from early childhood trauma and exposure to violence through to some sort of crisis point in their life,” Densley said.
He said this could be physical abuse, sexual abuse, abandonment or neglect or a parental suicide.
WATCH: 8chan speaks out after outages rock online messaging board
“There’s a whole host of these different sort of adverse childhood experiences that sort of mount up and become contributing factors,” he explained.
Next, Densley said it is “very common” among those who perpetrate mass shootings to reach an “identifiable crisis point.”
“I would almost think of it as often it’s a suicidal crisis and it is a point where people just feel like life has got too much,” he said. “They don’t want to live anymore, or they feel like their grievance is such that they have to take it out on the world.”
WATCH: AOC calls threatening violence against women ‘a warning sign for mass shooters’
He said they feel they have to take revenge on those who they believe to have harmed them.
He says these crisis points are articulated in some way and are often noticed by other people.
“But sometimes we just don’t join the dots together,” he said. “So if we’re a little bit more attuned to when people are struggling we can find a way to reach out and help them.”
WATCH: FBI warning about potential copycat attacks following Dayton, El Paso shootings
Densley said research suggests it is common for shooters to study other acts of terror, in order to seek validation for their motives.
This is why shootings sometimes occur on the anniversaries of other attacks, Densley said.
Lastly, Densley says all of the perpetrators they have studied had the means to carry out their plans.
“When we thing about access we think about access to the people and places that the perpetrator would like to attack,” he said.
“The other piece of this is access to the actual means to perpetrate the attack. And that speaks to guns in very simple terms. Without access to firearms, a mass shooting cannot occur.”
Preventing mass shootings
Denlsey says one step in preventing mass shootings from happening is to deprive potential shooters the means to carry out their plans.
He says this can be done through “sensible gun safety measures.”
Next, Densley says we need to think about the ways in which society responds to violence.
Society, he says, needs to avoid normalizing the attacks.
Subsequently, Densley says social media companies should be held accountable for spreading violent content.
WATCH: Vigil held outside NRA headquarters in Virginia to call for gun reforms in wake of El Paso, Dayton shootings
Next, Densley says better training is needed to recognize the signs of a person in crisis.
Lastly, Densley says ensuring communities are equipped with accessible, affordable health care, including mental health resources, is key to alleviating the trauma associated with adverse childhood experiences.
— With files from David Lao and the Associated Press